ANTARES-4 METADATA
1. PROJECT TITLE: Primary production and photosynthetic parameters in
the Subantarctic frontal region during the Antares-4 expedition in the
Southern Indian Ocean.
2. NAME OF PRINCIPAL INVESTIGATOR: Brian Griffiths
2.1 Address:
CSIRO Division of Marine Research
GPO Box 1538
Hobart, Tasmania AUSTRALIA 7001
2.2 Phone number: (61) 3 6232 5338
2.3 Fax number:
(61) 3 6232 5000
2.4 Email address: Brian.Griffiths@marine.csiro.au
3. BRIEF DESCRIPTION OF PROJECT
The major objectives of this project were to:
 Determine the photosynthetic parameters (the light-saturated rate of
carbon uptake, Pmax, and the initial slope of the curve, alpha, and the
photoinhibition parameter, beta) by measuring the carbon uptake by
phytoplankton as a function of irradiance (P vs. E). These parameters
will be used to model primary production by phytoplankton in the
Subantarctic and subtropical water masses, and in the Subantarctic
Front.
 .Determine the diel variation in photosynthetic parameters to allow
better estimates of modeled production to be made.
 Determine the effect of the addition of iron, silica, and nitrate on
photosynthetic parameters in the deck incubation experiment led by
Sedwick and Blain.
This investigation was carried out during the Antares-4 expedition in the
region between 42-47°S latitude and 60-66°E longitude. It forms part of
the French Joint Global Ocean Flux (JGOFS) research.
4. TITLES OF ANTICIPATED PUBLICATIONS
Primary production and photosynthetic parameters in and around the
Subantarctic front in the Kerguelen-Crozet Basin.
5. DESCRIPTION OF DATA
5.1 What did you measure and how did you do it (include references
for analytical methods)?
Photosynthetic parameters derived from P vs. E incubations were
measured at up to 7 depths in the upper 125m of the water column.
Water samples were taken from niskin bottles fitted with either silicon
rubber closures, or teflon-coated stainless steel springs. Photosynthetic
parameters were derived from the P vs. E curves following the
procedures given in Platt et al, (1980). The parameters were the
maximum photosynthetic rate (P*m ), the initial slope of the P vs. E
curve (alpha), and a photoinhibition parameter (beta). Parameters were
standardized by dividing by chlorophyll-a to obtain rates of carbon
fixation per unit of chlorophyll-a per hour. The chlorophyll-a data was
very kindly provided by Dr. M. Fiala. Dr. B. Delille kindly supplied total
DIC estimates, which were used in the calculation of uptake rates.
The P vs. I incubations were made following the Lewis and Smith
(1983) technique and the modifications described in Mackey et al.
(1995, 1997). The incubations took one hour, and the P vs. E
measurements obtained are close to the gross carbon uptake rate.
Temperature in the incubator was controlled by water baths, and
typically the shallowest 5 samples were incubated at the mixed layer
temperature and the deepest two samples at the average temperature
from these two depths. In practice, temperatures were usually within
1.5oC of the temperature at the sampling depth. The light field in the
incubator was calibrated at approximately 5 day intervals during the
expedition.
Estimates of primary production in the water column were obtained
using a simple model incorporating the photosynthetic parameters,
profiles of chlorophyll-a, extinction coefficients and daily PAR (see
Mackey et al 1995, 1997). The fluorescence profiles at each station
were converted to profiles of chlorophyll-a by calculating a linear
regression between the fluorescence at depths were chlorophyll-a
samples were taken.
The photosynthetic parameters were determined on the iron and
silicate , and iron and nitrate enrichment experiments, and the
experiments to determine the Ks value for iron of Sedwick and Blaine.
The same procedures were followed, except that column production
was not done. Due to space limitations in the incubator, only one of the
silicate or nitrate treatments was incubated at each time step. Both of
the controls, the plus iron, and plus iron and silicate treatments were
incubated, giving duplicate estimates for each of these treatments. The
photosynthetic parameters resulting from these experiments have been
included in the data being supplied by Blain, and will not be included
with the ctd results.
5.2 Sampling strategy:
A total of 30 ctd casts were sampled for production vs.
irradiance (P vs. E) curves, with 24 ctd casts sampling 7 depths per
cast. The remaining 6 casts sampled at two depths (surface and 50m
only), but were done at approximately 2 hour intervals to determine
how the photosynthetic parameters changed during the day. Sampling
depths were chosen to give maximum coverage through the water
column to a depth of 125m. Previous experience in the Southern
Ocean has shown that primary production below 125m is too low to be
measured by this technique. I tried to obtain samples from dawn, noon
and late afternoon ctd casts on at least two days per site.
In addition, 18 P vs. E experiments were made on the iron
enrichment incubation experiments of Sedwick and Blain.
5.3 Post-cruise data analysis/treatment required, and the time frame
for this.
I require DIC and chlorophyll-a data before the curve fitting to
extract the photosynthetic parameters. I anticipate having this data
prior to leaving the ship The curve fitting will take about one month.
The column production modeling requires calculation of the mixed layer
depth, and conversion of the fluorescence to chlorophyll profiles. Once
the CTD data is available, the mixed layer depth calculation and the
fluorescence to chlorophyll conversion should take several days, and
the modeling should take several weeks.
5.4 Error estimates, precision and accuracy of the data?
Because non-linear regression techniques are employed to obtain
the photosynthetic parameters, error estimates are difficult to obtain.
They will depend on the accuracy of the chlorophyll-a and DIC
estimates, as well as the phytoplankton uptake. The difference
between parameters obtained from duplicate estimates in the iron
incubation experiments is typically <10%. A more precise figure will be
given when the data are fully analyzed. A discussion of the accuracy of
the column production modeling is given in Mackey et al (1997), and is
considered to be about 30%.
6.
DATA DESCRIPTION
6.1 Data file structure:
The data file will be supplied in Excel 7 format. The first, follow
the recommended outline put together by Dominique Lefevre.
Details of the second data file, containing the column production
data will be supplied when the production modeling is done.
6.2 Explanation of headings, units used, abbreviations in data file.
Table 1
Pmax: light saturated production rate, in mg Carbon [mg
Chlorophyll-a]-1 hour-1.
Alpha: the maximum light utilization coefficient, or initial slope of
the P-I curve, in mg Carbon [mg Chlorophyll-a]-1 hour-1 [uE m-2 sec-1]-1.
Beta: the photoinhibition parameter. It is not present in all
samples. The units are mg Carbon [mg Chlorophyll-a]-1 hour-1 [uE m-2
sec-1]-1.
The intercept: this is really part of the curve fitting, and is used to
check for dark uptake of carbon. It does not feature in the modeling,
and has units of mg C [mg Chl a]-1 m-3 h-1.
The standard errors given are statistics derived from the curve
fitting, and are not error estimates on the parameter itself.
6.3 Estimate of when your data will be submitted to the data base.
Table 1 providing chlorophyll-a and DIC data is available at the end
of the cruise, in about one month. The production modeling requires
surface P.A.R. data in 10 minute averages, and CTD downcast data,
including temperature, salinity, and density with depth, and
fluorescence profiles before it can be done. Uncalibrated CTD data is
ok for the production modeling: I need to calculate the mixed layer
depth, and convert the fluorescence profiles to chlorophyll-a profiles
before the modeling can be done. Column production data should be
available in 3 months.
7. REFERENCES
Lewis, M.R. and Smith, J.C. A small-volume, short-incubation time
method for the measurement of photosynthesis as a function of irradiance.
Marine Ecology Progress Series 13, 99-102, 1983.
Mackey, D.J., J.S. Parslow, F.B. Griffiths, H.W. Higgins, and B. Tilbrook
Phytoplankton productivity and the carbon cycle in the western Equatorial
Pacific under ENSO and non-ENSO conditions. Deep-sea Research 44,
1951-1978, 1998.
Mackey, D.J., J.S. Parslow, H.W. Higgins, F.B. Griffiths, and J.E.
O’Sullivan. Plankton productivity and biomass in the western Equatorial
Pacific: Biological and physical controls. Deep-sea Research 42, 499-533,
1995.
Platt, T, C.L. Gallegos and W.G. Harrison. Photoinhibition of
photosynthesis in natural assemblages of marine phytoplankton. Journal
of Marine Research 38, 687-701, 1980.
Table 1:
Cruise
MD 113
Station
ANT4037
Niskin
24
Pmax
1.237
S.E.
0.12
Alpha
.O3214
S.E.
.0011
Beta
.0003
S.E.
.00001
Intercept
-.23
S.E.
.012